JP2862455B2 - Organic nonlinear optical material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical material used as a light control element in a wide range of fields such as an optical computer and an optical communication. The present invention relates to an organic nonlinear optical material having high activity and good crystallinity.

[0002]

2. Description of the Related Art Nonlinear optical materials include optical frequency conversion elements,
It has been practically used as an optical shutter, an EO converter, and the like. At present, inorganic ferroelectric crystals such as potassium dihydrogen phosphate (KDP) and lithium niobate are used as nonlinear optical materials. However, recently, attention has been paid to the magnitude of the nonlinear optical constant of the organic crystal, the speed of the nonlinear optical response, and the like, and the development of organic second-order nonlinear optical materials has been actively pursued.

As organic nonlinear optical materials for secondary effects, 2-methyl-4-nitroaniline (MNA), 3-methyl-4-nitropyridine-oxide (POM) and the like have been developed. The nonlinear constant is 50 of KDP
Double times.

It is widely known that an organic compound exhibiting such a strong nonlinear effect generally has an electron accepting group and an electron donating group with a π electron conjugated chain interposed therebetween. It is also known that second-order nonlinear optical materials must form crystals without inversion symmetry.

[0005]

Since one molecule of an organic nonlinear optical material is responsible for the optical nonlinearity, a molecule having an asymmetric center has SHG (second harmonic generation) activity in principle. When an SHG active molecule is crystallized and used as an optical element, the crystal often loses SHG activity as a whole. Therefore, to determine whether an organic material can be used as a nonlinear optical element, a molecular material must be actually synthesized, crystallized, and the optical nonlinearity must be evaluated.

The optical nonlinearity (supramolecular polarizability β) at the molecular level of an organic compound can be estimated from molecular orbital calculations. However, in order to enhance the optical nonlinearity of a single molecule, electron donation to a long conjugated system is required. What is necessary is just to introduce | transduce the substituent of the property and acceptability. For example, a stilbene-based molecule having a large supramolecular polarizability β at a molecular level was one of the typical organic nonlinear optical materials. However, according to the literature of the ACS series, this type of material has a center of symmetry in a crystalline state, and often becomes SHG inactive as a crystal.

[0007] Considering use as a wavelength conversion element, translucency in a molecular state or a crystalline state is an important factor. For example, stilbene-based materials often show a light absorption spectrum peak in the visible light region. Since the stilbene skeleton has a long conjugated system, introducing a strong electron-accepting substituent (nitro group, etc.) and a donating substituent (dimethylamino group, amino group, etc.) at the end of the conjugated molecule will absorb light in the visible light region. Expected to show. Therefore, it is a problem to weaken the strength of the electron-accepting or donating substituent, select the position of introduction of the substituent in the stilbene skeleton, and find a molecular material having no central symmetry as a crystal. The same can be said for the styrenic materials studied this time.

Further, the melting point of the conventional inorganic nonlinear optical material is about 1000 ° C., and it is thermally stable as an element.
However, there is a situation in which impurity diffusion occurs due to high-temperature growth and the optical damage strength is low. On the other hand, the melting point of an organic material is generally about 100 ° C., the temperature coefficient of the refractive index that determines the phase matching condition is large, and the use temperature tolerance as a wavelength conversion element tends to be low.

Accordingly, an object of the present invention is to provide an organic nonlinear optical material having high SHG activity and excellent thermal stability.

[0010]

The above object is achieved by an organic nonlinear optical material comprising a styrene derivative having a methoxy group at the 2,5-position and a cyano group and a thienyl group at the β-position. Can be.

Styrene compounds are characterized by a π-electron conjugate system longer than benzene and pyridine nonlinear optical materials. Therefore, in consideration of the trade-off relationship between the known nonlinear constant and the translucency, a very large electron accepting property (nitro group) and an electron donating property (dimethylamino group,
It is important to avoid the simultaneous introduction of a substituent of the amino group) at the end of the conjugated system. (Β-cyano) (β′-nitro) styrene represented by the following structural formula (II) in which a nitro or thienyl group is introduced as a substituent of electron accepting property near the center of the styrene conjugated system, and (III) For each molecular species of (β-cyano) (β′-2-thienyl) styrene represented by the following formula, the optical nonlinearity and the maximum absorption wavelength of one molecule were estimated by molecular orbital calculation (PPP method), and a thienyl group was introduced. Since the supramolecular polarizability β of the molecular species (III) thus obtained is three times as large, the thienyl group was examined as an electron accepting substituent. As the electron donating substituent,
A methoxy group was selected, and the position of the substituent to be introduced was examined.
In addition, in consideration of the size, rotational freedom, and rigidity of the substituent,
This is the reason for selecting the substituent.

As a result, the above-mentioned material exhibiting optical nonlinearity in a crystalline state has been found. In addition, the styrene derivative has high SHG activity and is therefore useful as a material for generating second harmonics.

[0013]

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[0014]

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[0015]

[Action] following structural formula (I) represented by 2,5-dimethoxy - (beta-cyano) (.beta. '-2-thienyl) styrene, maximum absorption wavelength lambda _max is at 382 nm (1,4-dioxane) is there. This has no large absorption in the wavelength region of blue light, and the SHG intensity by the powder method is twice as high as the urea ratio, and has sufficient nonlinear optical characteristics to solve the problem.

[0016]

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[0017]

The present invention will be described in more detail with reference to examples.

According to the present invention, 2,5-dimethoxy- (β
-Cyano) (β'-2-thienyl) styrene was synthesized as follows.

2,5-dimethoxybenzaldehyde
After dissolving 7 g (0.016 mol) in 150 ml of ethanol, thiophen-2-acetonitrile 2.0 g
(0.016 mol) was added. In it, 10 ml of ethanol solution in which 0.7 g of sodium ethylate was dissolved
Was added dropwise.

After stirring the solution at room temperature for 6 hours, the resulting precipitate is filtered and washed with methanol to give the desired compound represented by the above structural formula (I), 2,5-dimethoxy (β-cyano). ) (Β'-2-thienyl) styrene.

The yield was 68%. The maximum absorption wavelength is 382 nm (in 1,4-dioxane),
Melting point was 88 ° C. based on DSC measurement.

This is described in MAP (literature; JL Ouda).
r and R.R. Hierle, J .; Appl. Phys
s. , 48 (1977) 2699). Next, when the obtained fine powder crystal is irradiated with a Nd: YAG laser (wavelength = 1.64 μm), a second harmonic (SHG) is generated, and a wavelength (532 n
m) green light was observed. This SHG intensity was twice the urea ratio, and it was confirmed that the SHG efficiency was stronger than that of urea.

Further, a plate-like crystal was easily obtained by a recrystallization operation from normal hexane, and a single crystal could be formed as a seed crystal.

[0024]

COMPARATIVE EXAMPLE The present inventors have 2-methoxy- (β-cyano) having a thienyl group and having a methoxy group introduced at the 2- or 4-position of the α-phenyl group and represented by the following structural formula (IV). (Β′-2-thienyl) styrene or 4-methoxy- (β-cyano) represented by the following structural formula (V)
(Β'-2-thienyl) styrene and (β-cyano) represented by the following structural formula (III) in which nothing is introduced.
Each molecular species having (β'-2-thienyl) styrene was synthesized to obtain a crystal.

[0025]

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[0026]

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[0027]

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However, when these compounds were evaluated by the powder method, they were SHG-inactive.

[0029]

According to the present invention, 2,5-dimethoxy-
The organic nonlinear optical material composed of (β-cyano) (β′-2-thienyl) styrene has a high melting point of 88 ° C. and is thermally stable. Furthermore, the absorption edge is on the short wavelength side and the SHG is high.
Since it shows activity, it can be used in a wide range of fields as a nonlinear optical element.

Further, by using an organic material excellent in such optical nonlinearity, translucency, and temperature tolerance of the phase matching condition, it is possible to replace the expensive inorganic nonlinear optical material with an equivalent characteristic. An organic nonlinear optical material can be provided at a low price.

[Brief description of the drawings]

FIG. 1. 2,5-Dimethoxy- (β-cyano) (β′-
It shows the relationship between wavelength and absorbance in 1,4-dioxane of (2-thienyl) styrene.

Claims (2)

(57) [Claims] 1. An organic nonlinear optical material comprising a styrene derivative having a methoxy group at the 2,5-position and a cyano group and a thienyl group at the β-position. 2. A material for second harmonic generation comprising a styrene derivative having a methoxy group at the 2,5-position and a cyano group and a thienyl group at the β-position.